Traditional powdery human hair bleaching composition generally includes solid peroxide and some pulverulent particles. The pulverulent particles can be alkaline agent, thickeners, or surfactants. Most commonly, particles such as, alkaline silicate, silicon dioxide, alkaline stearate and alkaline carbonate are used. These ingredients are commonly used as dry powders which must be mixed with aqueous solution or emulsion of hydrogen peroxide before they are applied to hair for coloring. During handling and mixing, fine dusts are generated by the collision and abrasion of powders with each other. The fine dusts of persulfate compounds and alkaline silicate can irritate human eyes, respiratory canals and mucous membranes. More and more research has been done to investigate the association between asthma and exposure to hair bleaches among hairdressers.
To overcome such disadvantages, several patents have disclosed various compositions and methods to make dust free bleaching powder. U.S. Pat. No. 4,170,637 discloses hair bleaching compositions that include an intimate mixture of at least one particulate persulfate salt and at least one alkali silicate with 30%-70% by weight of an anhydrous organic carrier base of the total mixture. These compositions are not free-flowing powders, but instead as paste or cream, they are much more difficult to manufacture and pack for use.
In general, various oil and wax can be used to produce dustless bleaching compositions as long as it will not affect the bleaching and dissolving properties of the bleaching composition during application. U.S. Pat. No. 5,891,423 discloses the treatment of dust-forming bleaching powder with about 10% to 25% by weight of the inert oil, while the preferred range is from about 14% to 20% by weight to the total composition. U.S. Pat. No. 5,989,530 discloses another type of hair bleaching composition that includes at least one solid peroxide compound, at least one powdery carrier material, and about 2.5% to 25% by weight of oil and/or liquid wax, while the most preferred range is around 8% to 12% by weight of the total composition. U.S. Pat. No. 5,866,107 discloses the testing results of poor thixotropy property of prior art commercial products when 10% by weight of mineral oil is added to the bleaching compositions. Extra embrocation or wetting is then required to make the hair bleaching more effective and even due to the poor thixotropy. The unstable oil emulsion is formed during mixing of the water insoluble oil and/or wax with the aqueous solution of hydrogen peroxide. It takes a longer time for the paste to become in a stable form. At the same time, the oil and/or wax residues remain on the hair after application, which is difficult to wash off. Therefore, the use of oil and/or wax should be minimized in the production of the dust free bleaching powders.
The amount of oil for producing dust free bleaching compositions depends on many parameters such as the properties of the oil, the oil adsorption property of powder ingredients in the bleaching compositions and the process for mixing the oil into the bleaching compositions. The oil should be a liquid with a low viscosity at a temperature below 30 degrees so that it can be easily sprayed into the powder ingredients in the bleaching composition. The use of powder ingredients with high extent of oil adsorption property should be avoided as excess oil may be adsorbed on the internal surface area of the powder ingredients. The excess oil may be released out during mixing with the hydrogen peroxide solution in the hair bleaching application.